With reference to FIG. 7, a re-connection process in a mobile communication system of the LTE (Long Term Evolution) scheme will be explained.
As illustrated in FIG. 7, in step S501, when a mobile station UE detects a quality deterioration of a radio link (specifically, an RRC connection) established with a radio base station eNB1, the mobile station UE activates a timer T310.
In step S502, when the quality deterioration of the radio link is not recovered before the timer T310 expires, then the mobile station UE detects a failure in the radio link (RLF: Radio Link Failure) and activates a timer T311.
During a time that the timer T311 is activated, the mobile station UE performs a cell selection process. And, when a specific cell is discovered, the mobile station UE attempts to establish a radio link with a radio base station that manages the specific cell. At this time, when a “UE Context” of the mobile station UE is managed in the specific cell, then the establishment of the radio link is successful.
In step S503, when the specific cell is not discovered during a time that the timer T311 is activated, when the “UE Context” of the mobile station UE is not managed in the discovered cell, or when an inter-RAT cell is discovered during a time that the timer T311 is activated, then the mobile station UE is transitioned to an idle state (RRC_Idle state).
Thereafter, in step 504, the mobile station UE starts camping on a cell under the control of a radio base station eNB2.
In step S505, the mobile switching center MME does not know that the mobile station UE has started the camping on the cell under the control of the radio base station eNB2, and therefore, the mobile switching center MME transmits downlink data destined to the mobile station UE, to a radio base station eNB1. Therefore, the downlink data destined to the mobile station UE is lost without reaching the mobile station UE.
In step S507, the radio base station eNB1 releases an S1 connection with the mobile switching center MME for the mobile station UE, because there is no response, within a predetermined period from the mobile station UE, to an uplink synchronization request signal transmitted to the mobile station UE in step S506.
In step S508, the mobile switching center MME transmits a paging signal to the mobile station UE.
In step S509, in response to the received paging signal, the mobile station UE establishes a radio link with the radio base station eNB2 by transmitting a service request to the mobile switching center MME.
In step S510, the radio base station eNB2 transmits downlink data via the radio link established in step S509.